Brushless motors are well known. Conventionally, these motors comprise a housing rotatably supporting a rotor carrying a plurality of permanent magnets arranged in pole pairs. These magnets supply the field flux. A plurality of stators are are arranged about the rotor. Each stator has stator windings such that the interaction of current passing through the winding with the flux of the rotor magnets produces torque if the current through each stator winding is timed correctly with respect to rotor position.
Typically, brushless motors provide the necessary commutation position feedback information to a motor controller through the use of either an optical encoder mounted on the end of the motor or through Hall effect sensors placed in close proximity to a disc having a magnetic pattern thereon which rotates with the rotor.
U.S. Pat. No. 4,931,712 to DiGiulio et al. entitled Multiple Channel Servo Configuration discloses an arrangement for driving brushless motors in a mailing machine environment.
U.S. Pat. No. 5,010,282 to Moberg suggests the use of an integrated circuit device which eliminates a sense resistor for the motor current by detecting the drain-to-source voltage of a power FET and generating a feedback current that is proportional to it.
U.S. Pat. No. 4,814,674 also teaches the use of a monolithic integrated circuit which includes a pulse shaping circuit for shaping the slope of the driving pulse edges.
U.S. Pat. No. 4,544,868 teaches a pulse-width modulation circuit to monitor the current supplied to the motor and to interrupt motor energization whenever the current rises above a reference level. The circuit is also used to provide regenerative braking whenever the direction of motor rotation is to be reversed.